Réponse :
15/21 = 3x5 / 3x7 == 5/7
81/45 = 9x9/9x5 = 9/5
2/10 = 1x2 / 5x2 = 1/5
3/27 = 3x1 / 3x9 = 1/7
60 /123 = 3x20 / 3x41 = 20/41
30/75 = 5x6 / 5x15 = 6/15 = 2x3 / 5x3 = 2/5
Explications :
